1. Field of the Invention
The present invention relates to telecommunication systems and, in particular, to systems offering general packet radio services (GPRS).
2. Description of the Related Art
Mobile systems include a plurality of mobile user equipment (UE) eg mobile telephones moving from one domain to another. Each domain includes a radio network controller (RNC) and/or base station controller (BSC) and an associated serving GPRS support node SGSN to handle the connection of each mobile UE in its domain with any other network. Each RNC can include a third generation UMTS (universal mobile telephone system) RNC or a second generation GPRS, BSC.
When a mobile UE moves to another domain, the RNC and SGSN in that other domain take over the handling of the connection between the mobile UE and the mobile network. An example of such a procedure is serving RNC (SRNC) relocation in which the RNC is in control of the call. The handover procedures can often result in a diminished service during the handover period.
The mobile system shown in FIG. 1 comprises an array of radio network controllers (RNC) 2 for controlling the connection of mobile UE's 6 with a the network.
Each RNC 2 is connected to a group of node B's4. Each node B 4 is able to communicate with one or more mobile telephones 6 within its territory.
Each RNC 2 is in turn connected to a corresponding serving GPRS support node 10 via an Internet protocol (IP) network 8. The SGSN 10 is connected to home location register (HLR) 12 containing user information such as user identity and call service requirements. The SGSN is thus able to verify the identity of the user for security purposes and is also able to update the HLR with the current location of the user. Other functions are also possible.
The SGSN 10 is able to connect the mobile UE with other packet data networks (not shown) using a gateway GPRS support node (GGSN) 14.
Where a mobile telephone moves from being under the control of one (current) RNC 2 to another (target) RNC and the target RNC 2′ does not share the same SGSN 10 with the current RNC, then a handover must take place from the current SGSN handling the mobile to the target SGSN 10′ associated with the target RNC. The current SGSN 10, through the IP network, communicates with the target SGSN 10 to effect its handover to the target RNC 2. The target SGSN 10′ must then contact the HLR 12 to re-establish the user identity and update the HLR 12 on user location.
Where real-time service is required, eg voice service, this procedure is likely to provide an undesirable interruption in communication.
This problem is solved with the system shown in FIG. 2. In FIG. 2, parts similar to those in FIG. 1 are similarly referenced but with the suffix A. It is an object of the present invention to provide an improved telecommunication system.